Jani Sainio

Single‐Shell Carbon‐Encapsulated Iron Nanoparticles: Synthesis and High Electrocatalytic Activity for Hydrogen Evolution Reaction

Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single-shell carbon-encapsulated iron nanoparticles (SCEINs) decorated on single-walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non-noble-metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications.

Predominant (6,5) Single-Walled Carbon Nanotube Growth on a Copper-Promoted Iron Catalyst

We have developed a magnesia (MgO)-supported iron-copper (FeCu) catalyst to accomplish the growth of single-walled carbon nanotubes (SWNTs) using carbon monoxide (CO) as the carbon source at ambient pressure. The FeCu catalyst system facilitates the growth of small-diameter SWNTs with a narrow diameter distribution. UV-vis-NIR optical absorption spectra and photoluminescence excitation (PLE) mapping were used to evaluate the relative quantities of the different (n,m) species. We have also demonstrated that the addition of Cu to the Fe catalyst can also cause a remarkable increase in the yield of SWNTs. Finally, a growth mechanism for the FeCu-catalyzed synthesis of SWNTs has been proposed.

Ultra-narrow metallic armchair graphene nanoribbons

Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N=3m+2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N=5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ∼100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.

A novel method for metal oxide nanowire synthesis.

Nanowires (NWs) of metal oxides (Fe(2)O(3), CuO, V(2)O(5) and ZnO) were grown by an efficient non-catalytic economically favorable method based on resistive heating of pure metal wires or foils at ambient conditions. The growth rate of iron oxide NWs exceeds 100 nm s(-1). Produced NWs were typically 1-5 microm long with diameters from 10 to 50 nm. The produced metal oxide NWs were characterized by means of SEM, TEM, EDX, XPS and Raman techniques. The field emission measurements from the as-produced CuO NWs were found to have a threshold field as low as 4 V microm(-1) at 0.01 mA cm(-2). The formation mechanism of the NWs is discussed.

Halogen-bonded mesogens direct polymer self-assemblies up to millimetre length scale

Aligning polymeric nanostructures up to macroscale in facile ways remains a challenge in materials science and technology. Here we show polymeric self-assemblies where nanoscale organization guides the macroscopic alignment up to millimetre scale. The concept is shown by halogen bonding mesogenic 1-iodoperfluoroalkanes to a star-shaped ethyleneglycol-based polymer, having chloride end-groups. The mesogens segregate and stack parallel into aligned domains. This leads to layers at ~10 nm periodicity. Combination of directionality of halogen bonding, mesogen parallel stacking and minimization of interfacial curvature translates into an overall alignment in bulk and films up to millimetre scale. Upon heating, novel supramolecular halogen-bonded polymeric liquid crystallinity is also shown. As many polymers present sites capable of receiving halogen bonding, we suggest generic potential of this strategy for aligning polymer self-assemblies.

Topographic and electronic contrast of the graphene moire on Ir(111) probed by scanning tunneling microscopy and noncontact atomic force microscopy

Epitaxial graphene grown on transition-metal surfaces typically exhibits a moir´e pattern due to the lattice mismatch between graphene and the underlying metal surface. We use both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) to probe the electronic and topographic contrast of the graphene moir´e on the Ir(111) surface. STM topography is influenced by the local density of states close to the Fermi energy and the local tunneling barrier height. Based on our AFM experiments, we observe a moir´e corrugation of 35 ± 10 pm, where the graphene-Ir(111) distance is the smallest in the areas where the graphene honeycomb is atop the underlying iridium atoms and larger on the fcc or hcp threefold hollow sites.

Unusual Dual Superlyophobic Surfaces in Oil–Water Systems: The Design Principles

Thermodynamically unusual surfaces that possess two contradictory wetting properties, i.e., underoil superhydrophobicity and underwater superoleophobicity, are prepared by the combination of re-entrant topography and delicately matched surface chemistry. The preparation of such extraordinary surfaces relies on two key design criteria and employs a metastable state effect in solid-oil-water systems.

Structure and local variations of the graphene moiré on Ir(111)

We have studied the incommensurate moire structure of epitaxial graphene grown on iridium(111) by dynamic low-energy electron diffraction [LEED I(V)] and noncontact atomic force microscopy (AFM) with a CO-terminated tip. Our LEED I(V) results yield the average positions of all the atoms in the surface unit cell and are in qualitative agreement with the structure obtained from density functional theory. The AFM experiments reveal local variations of the moire structure: The corrugation varies smoothly over several moire unit cells between 42 and 56 pm. We attribute these variations to the varying registry between the moire symmetry sites and the underlying substrate. We also observe isolated outliers, where the moire top sites can be offset by an additional 10 pm. This study demonstrates that AFM imaging can be used to directly yield the local surface topography with pm accuracy even on incommensurate two-dimensional structures with varying chemical reactivity.

Maghemite nanoparticles decorated on carbon nanotubes as efficient electrocatalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) is a critical reaction in electrochemical water splitting and rechargeable metal–air batteries to generate and store clean energy. Therefore, the development of efficient and low cost electrocatalysts for the OER with high activity and stability is of great technological and scientific interest. We demonstrate here for the first time that maghemite (γ-Fe2O3) nanoparticles decorated on carbon nanotubes (CNTs) function as low cost, highly active and durable OER electrocatalysts. The material generates a current density of 10 mA cm−2 at overpotentials of 0.38 and 0.34 V in 0.1 and 1 M NaOH, respectively. These values are comparable to those of the best OER electrocatalysts reported so far. Moreover, γ-Fe2O3/CNTs show a stable performance at a potential of ∼1.64 V vs. RHE during 25 h stability tests. The γ-Fe2O3 nanoparticles are formed from carbon encapsulated iron nanoparticles (CEINs) during the first OER measurements of the CEIN/CNT electrode. The CEIN/CNT material itself is synthesized by a fast and low cost floating catalyst chemical vapor deposition method in a one-step synthesis with a similar growth process to that of CNTs.

Optical properties of silicon nanocrystals in silica: Results from spectral filtering effect, m-line technique, and x-ray photoelectron spectroscopy

A new class of Erbium doped glasses with compositions xNa2O–(60 - x) PbCl2–40P2O5 (x = 0, 10, 20 and 30) were fabricated and characterized for optical properties. Absorption spectra were analyzed for important Judd–Ofelt parameters from the integrated intensities of various Er3+ absorption bands. A systematic correlation between the Judd–Ofelt parameter Omega.2 and the covalent nature of the glass matrix was observed, due to the increased role of bridging oxygens in the glass network. Photoluminescence (PL) and its decay behavior studies were carried out for the transition 4I13/2 to 4I15/2. The PL broadness and life times were typically in the range of 40–60 nm and 2.13–2.50 ms, respectively. These glasses show high transparency, high refractive index, shorter life times and, most importantly, these glasses were capable of being doped with larger concentrations of Er3+ (up to 4 wt%). Optical performance of these doped phosphate glasses suggesting the suitability of these glasses for optical fibre/waveguide amplifiers.